Electron-discharge device



May 11 1954 w. c. BROWN ET A1. 2,678,407

ELECTRONv-DISCHARGE DEVICE Filed Jan. 4, 1950 2 Sheets-SheetI l .....rnglf May 11, 1954 w. c. BROWN ET AL 2,678,407

ELEcTRoN-DISCHARGE DEVICE Patented May 1l, 1954 sehelk, -Wetentewn Mess .sssigners-.to ReytheonManiifacturing Company, yNewton,.l\.\[ass.,

.a corporation of, D elaware -.Application*January 4, 1950,4 Serial No. 136,714

` 15 lClaims. l

-..'lhisinventionreletes:to*eleetronrdiseharseade- Vlees,- end .more nartieuial'lyto .mierowayefoseilation generetingdevieesrof .themeenetron type.

. Magnetrons arensually operated.y at.; one.. oie plurality of discrete frquenciesknown. asrnodes. 'lheg-most common, operating mode ris knovqlfi as the. `snede 1;Where...e1.ternete enodernembers. are maintained at the same instantaneguspotential, and the oscillating potential occurs between adjacent anode members. lnwmodes adjacent the 1r mode,- alteinate anode members varygfrom each vother in potential,v said varying. potentials formingl a substantial sinusoidal Wave traveling around the anode structure. y A resonant mode occurs when gthe Waver-,traveling around the anode structure returns to itsstarting point. atsuch aM phase thatit will reinforce itself. Sinhcejthe aforesaid phase varies considerably Y, Y quencmand reinforcement and hencepscillatipn occur when -the instantaneous vWave, voltages `of the anode structure vary through a multiple of 3.60, degrees duringone; traverse around the ande structure, it may.. bessen-that. e nluralitrof possible osci11ation modes exist, V.sa id, modes.A being separatedf by diseretefrequencies.

""When percentage, 'frequency separation between the v.operating Inode such aswthe. 1r lmode and an "adjacent mode is,v undesirably small,l the magnetronKWill tend to oscillatein ,the adjacent mode and sap energy froml the desired operating mode. Further if theload impedance into. the'magnetron is Working varies; someyvliat,` the magnetron lrnaysnift-its frequency fromthe-.desired operatngmode to theadjacentmode.

In ordertoincreaseN the powerv output. from a, magnetron, the ynumlcger of anode.,.membersI must, in generabbeincreased, sincethepower output per anode member is limited by the heat dissipating ability; of the; anode member. However, an analysis., of the anodestruoture of a conventional, double strapped -cavity magnetron shows that areincrease of the anode members results a in a, .deorease in., modes. separation. 'fhus, the. l.rnaxirninn -power output -Whien ,eoiild v'eloped by magnetron structuresgras,l .1i ri,

designs, been limited by the available 'mode separation of the magnetron.

The present invention gdisolgsesa noveltniagnetl'on anode g'strlieturef-irneiein zthemede :seneration is considerably greater than in conventional designs. This ismacomplislied by making the; anode members 0f .hollow tubes, 5 eah 4,tube

beinggsuppprted at .two `points :substantially a halfnwavenleng-th apart. The tubes rare, spaed 5 around the axis of the-.ineenetren endfelefnnielieitnerete. The midnointsfef--ediaeenttubes/.ere rkinnef'edA to` the opposite.- surfaceswof .aradial transmission `linewnose .effect is. toinereese f-.ne inode .separation of;.the1Inasnetronand,Y .in .eddition. fteeot as. .en output Coupling .dence The redini trans.n lissioirl line. is snorted. silbstentielly. e eue-liter. were t length... away. fromv the anodeA lrnei'nbersmso l .that it,.wi11y` resonate.at` the Seine frequency. es.. the.v anode; members ,.By the nsepithis. stinoture, a larger .number ofrenes may be used Without encountering undesirably sinalz;Inode..senereti0n addition, sinoe....the anode members. are A.in

.in-:0i: tnb.es,...e-.09lent.rney beeireulated throne, tile t.l 1.bes, -therebyy .further .inereasing the, power which, may. bej generated p er, anode membel'- :.A1S0, .eOndtiOns are favorable gior newerfeeneration by interaction .ortheeleetron Streemgor; a .relatively ,large distance. on .each side: Oigihe. mdnoints, soi, the vanode...members .so that anextenled cathode may be.used,. .whereby a larger surfaced each anode, member is. presented, totl 1eelec tr,on streaml than was heretofore,.nossiblathrough l vthe, `resultant increase .-in thenower. .dissi atingability of the anode mem- @e and., en attendant .increase `in the power. ont- Iu forfesh, snede .meinber- Ot-her, and Lnirther, adyantagesrof this `inventientwill be .apparent-es thetdesenpnonthereof progrv ses, reference. tisei'rlg. had. to.- the. .aecom- Danying drawings, .Wherein:

. -Eig' 1- illustrates., e vlongitudinal....erossfseeiieiiel .newA 0f -Ole sessies of.the...devise-embody- A ing .thisfinven'tion 47Vtaken alongfline l-,I ,of

2... 111.114.strates e transverse,.- orossgseetional fr he. @Vice inzFia; 1.... taisen-fa19ng characteristics of the device shown in Figs. 1

. and?.

I .ii-:iferringgnow. to Figs. 1 and 2, there is shown a magnetron structure comprising a plurality of parallel, tubular anode members I!) which are spaced around the axis of the magnetron parallel thereto. The upper ends of the tubes I extend through an upper end plate II which is tightly sealed to tubes I by any desired means, such as soldering. The lower ends of tubes I0 extend through a lower end plate I2 and are sealed therein in a manner similar to their sealing in upper end plates |I. The distance between upper and lower end plates II and I2 is made substantially equal to a half wave length of the desired operating frequency of the magnetron.

A radial transmission line comprising upper and lower parallel, planar conducting members I3 and I4, respectively, is connected to substantially the midpoints of the anode members Hi in the following manner. One set of alternate anode members is attached to the upper guide member I3, while the other set of alternate anode members, which comprises anode members adjacent the anode members of the nrst set, is connected to the lower guide member lli. Guide members I3 and |11 are in the form of disks, substantially a half wave length in diameter, extending inwardly from the anode members I6 to the axis of the magnetron,

An output coupling member I5 is connected to the radial wave guide. The output coupling comprises a tube I6 extending through an aperture in the center of upper guide member I3 and connecting to lower member Id. Tube IB extends upwardly through and is sealed to upper end plate I I. Inside tube I6 and coaxial therewith is a central conductor I'I, one end of which extends through an aperture in the side wall oi tube I6 between guide members I3 and I4 and is welded to member I3 thus forming the pickup loop. The other end of conductor II extends out through the end of cylinder |t and is insulatedly supported therefrom as, for example, by a glass seal I8.

Surrounding the entire group of anode members, coaxial with the axis of the magnetron and spaced from said anode members, is a cathode structure I9 comprising a metallic cylinder 20, the inner surface of which is coated with electrcn-emissive material 2|. Around cylinder 20 there is wound a heater coil 22 which is imbedded in a coating of insulating material 23 such as, for example, Alundum. The cathode structure I9 is supported at its upper and lower ends by a pair of ceramic rings 24 and 25, respectively.

Lower ceramic ring 25 rests upon lower end plate |2, and upper Vceramic member 24 is resiliently urged downward against the top of the cathode structure I9 by means of an annular spring 26 positioned between ceramic ring 24 and upper end plate II. One end of the heater wire 22 is connected to the cylinder 25, as by welding, and the other end of the heater wire is connected to a lead-in conductor 2l which extends through lower ceramic member 25 and a cylindrical member 28 sealed into an aperture in lower end plate I2. Conductor 21 is insulatedly supported from cylinder 28 by a glass seal 29 at the end of member 28. The cylinder 20 is connected to a lead-in member 3Q which extends through ceramic member 25 and a tubular member 3| sealed in an aperture in lower end plate I2. Conductor 30 is insulatedly supported with respect t0 jdRc 4 member 3| by means of a glass seal 32 in the end of member 3|.

Surrounding the cathode I9 and ceramic supports 24 and 25, there is a cylindrical member 33 which is attached to both upper and lower end plates I I and I2, as by soldering, thereby producing a gas-tight enclosure within the magnetron. A magnetic held is produced in the space between anode members IIJ and cathode cylinder 20 by any desired means, such as a coil 32, wound around the outside of cylinder 33 and concentric therewith, through which a suitable direct current is passed. Anode members I5, which are hollow, pass out through end plates and |2 and terminate in upper and lower hollow annular rings 35 and 36, respectively. Upper ring 35 has an inlet pipe 31 connected thereto, whereby a coolant such as, for example, water, may be introduced into the ring 35 and thereby fed through the anode members I0. The coolant upon passing through anode members I0 will collect in lower ring 3S and may be carried off by an exhaust pipe 38 connected thereto.

With a suitable heater voltage applied between conductors 21 and 3, a suitable anode voltage applied between conductor 3|] and the anode structure, and a suitable magnetic field applied by means of a current through coil 34, the magnetron will oscillate. An analysis of the mode separation which may be achieved by this structure may be made as follows.

The voltage distribution around the anode members of the magnetron will be sinusoidal and of the form EzEmax Sin fLb where E is the instantaneous voltage generated during a traverse around the anode structure, Emax is the maximum voltage generated during the traverse around the anode structure, n is the number of the mode, being 0 for the 1r mode7 and l for the mode adjacent the 1r mode etc., and p is the physica1 angle of rotation around the axis of the anode structure.

The voltage distribution in the radial transmission line for a traverse around all the anode members is also of the form E=Emax Sin fl/KP (2) where n denotes the number of complete cycles of variation of voltage in the angular direction around the radial transmission line. Therefore, in corresponding modes where n=n, the instantaneous potential of the anode members is similar to the instantaneous potential of the wave traveling in the radial wave guide with the result that impedance matching between the wave guide and the anode members is uniform around the anode members.

Solutions of the input impedance to the radial transmission line may be obtained from field theory. For the rr1,'=0 mode, the total input impedance for a radial transmission line, which is short circuited at its output end, is:

JoUca) For the 1L=1 mode, the input impedance for a radial transmission line, which is short erculted at the output end, is:

where Je( indicates Bessel Function of 'first kind and 'n the order. No( indicates Bessel Function of second kind and n the order. sgniies the derivative. k=21r/. KLV-.wave length. a`==o`ut`er radius. b=inner radius. d=separation of plates.

The total input impedance to the magnetron anode members, as seen by vtheradial transmission'li-zi'e., is

wherel Z. is the total anode input impedance;

Z0- is the characteristic impedance of a pair of adjacent anodemembers; and

N. isthe number of anode members.

plottof Formulas 3, i and 5 appears in Fig. 4 wherein impedance is plotted along the' axis of ordinates, and wave length in centimeters is plotted along the axis of abscissae. The curve Iltis'aplotof r the impedan'c'eof the'radial transmission' line vs. frequency for the 11"--0- mode given by Equation 3. It may be seen that this curve' goes to infinity at a wave length of 10 centimeters which 'is the frv mode. Curve 40 is a plot-of'theimpedanceof the anode members vs. frequency as given by Equation 5. As shown here, positivev'alues lof the anode impedance are plotted as negative" impedances and negative values are plotted as positive impedances. This curve" also is discontinuous by passing to infinity at the 1r mode. Curve' 4l is a plot 'of the impedancevs; wave` length for a mode of propagation in the radial transmission line which is the n=1 mode given by Equation 4. This mode has an impedance characteristic 'which is discontinuous bypassing to linrlnityat a wavelength somewhat greater than that of 'the 1r mode'. For this reason the curve 4l intercepts the-curve 40 at a wave length greater than that of the 1r mode, as shown by poi-nt42. Atthis point the reactive impedance ofthe radial transmission line which is positive isY `just equal and opposite to the reactive impedance of the anode members which is negative although plotted here asV positive, and the re'- sultant sum of these reactive impedances is zero thus'deiining a condition of resonance. As may bewseen from theM graph, this condition of resonanceo'ccurs at approximately 8.6 centimeters orapproximately 1.4 centimeters away from the 1r 'model lThe mode separation ratio is, therefore, 114 to: 10 or 14 per cent. This is a considerably greater mode separation than can be obtained in -a conventional double strapped magnetroh.- c

Referring now to Fig. 3, there is shown a modiilcation of the device shown in Figs. 1 and 2, wherein the cathode is positioned inside the anodenembers and theY radial transmission line isifpositioned outside the anode members. The anode members, coolant intake and exhaust structure; and magnetic field structure are similar tolith'at of Figs. 1 and l2. However, a cathode isfpositioned inside the anode members l0 insteadofthe radial transmission line. The cathode comprises a metal cylinder 43 spaced from anode memlxns Illand surrounded thereby. The outerrsurfaceofi cylinder 43 is covered by electron'emissive material. The upper and lower ends of cylinder I3 are closed by upper and lower end plates 45 and yMi, respectively. The lower end plate 46 has attached to 'the center thereof a hollow support cylinder 41 which extends through a metal cylinder All sealed into van aperiture in the lower end plate l2. Cylinder is rigidly supported with respect to cylinder v4l! by means of-a glass seal 49. Inside cylinder y th is wound a heater coil 4'4, one end `o'l which' attached, as by welding, to cylinder 43, and the other end of which is connected to a leadei'ii member 45 which extends through cylinder `41 coaxial therewith, and is rigidly supported with respect thereto by means of -a glass 'seal "50. The support and lead-in structure of the cathode's of Figs.- 1 and 2, as well as the cathode "of Fig. 3 just described, are shown by way of example' only, and any desired cathode structure which 'will' .produce the desired electron 'emission adac'en't the anode members le may bev used.

Positioned outside the anode members l0 is the .radial transmission line comprising upper andlower planar members `5! and 5-2, respecti l, upper member 5l being connected to one vgroup' of alternate anode members adjacent the midpoin'ts thereof, and the lower member 52 being connected to the other group of alternate anode members inY a manner similar to that described in connection with the radial transmission line of Figs.V l and 2. The outer edges of members 5I and 52 are connected to the cylinder 5313i comi prising the envelope of the magnetron. The tance between the cylinder 33Y and the anode members along the transmission line is made substantially equal to afquarter wave length at the desired loperating frequency. Thus, the

transmission line, being -sho'rted at its outer end by cylinder 33, will resonate at thesame fre'fquency as ywill adjacent pairs of anode members I9, thereby producing anl oscillatory structure. An output coupling loop 53 may be inserted through cylinder 33' in a well-known manner.

An` analysis of this structure may be under-Y taken by the same procedure as that illustratedY in connection with Figs. l and 2. However, the mode separation produced by this structure vwill be somewhat less than that produced by' the structures of Figs. 1 and 2.

This completes the description of the particular' embodiment of the invention disclosed herein by way of illustration. However, many modif-low tions thereof will be apparent topersons skilled in the'art without departing from the spirit'and scope of this invention. For example, theariode` members could be supported at one end only and be made substantially a quarter wave length long, or any multiple thereof, and the radial transe' mission line could be made other multiples of a quarter wave length, and other coupling means could be used -for extracting power from 'the de# Ivice. Therefore, applicant does not Wish to be restricted to the'specic details of the' species of the invention illustrated hereinexcept as drained: by the appended claims.

What is claimed is:

1. An electron discharge device comprising acathod'e, an anode structure spaced from vsaid` cathode, a radial transmission line comprising substantially planar members connected' to said anode structure for coupling energy between said' anode structure and said transmission line, ad= jacent anode members being connected to opposite bounding surfaces only of said transmission line, and means adjacent said anode structure for producing a magnetic eld between said 'cathode' 7 and anode structure perpendicular to the direction of motion of electrons from said cathode to said anode structure.

2. An electron discharge device comprising a cathode, an anode structure spaced from said cathode comprising a plurality ol anode members, and a radial transmission line comprising a pair of substantially parallel planar conductors, adjacent anode members being connected to opposite bounding surfaces only of said transmission line.

3. An electron discharge device comprising a cathode, an anode structure spaced from said cathode comprising a plurality of anode members, each of said anode members extending in a direction parallel to the electron emitting surface of said cathode for a distance substantially equal to a multiple of a half wave length of the operating frequency of said device, and a radial transmission line connected to said anode members with adjacent anode members being connected to opposite bounding surfaces only of said transmission line for coupling energy between saidv anode structure and said transmission line.

4.An electron discharge device comprising a cathode, an anode structure spaced from said cathode comprising a plurality oi` anode members, each of said anode members extending in a direction `perpendicular to the electron path between said cathode and said anode structure for a distance substantially equal to a multiple of a quarter` wave length of the operating frequency of said device, and a radial transmission line Aconnected to said anode members adjacent the mid points thereof, adjacent anode members being connected to opposite bounding surfaces only of said transmission line.

5. An electron discharge device comprising a cathode, an anode structure spaced from said cathode comprising a plurality of anode members, a radial transmission line comprising a pair of substantially parallel disk portions, adjacent anode members being connected to opposite bounding surfaces only of said transmission line, and means adjacent said cathode for producing a magnetic eld between said cathode and anode structure, and perpendicular to the direction of motion of electrons from said cathode to said anode structure.

6. An electron discharge device comprising a cathode, an anode structure spaced from said cathode comprising a plurality of anode members, each of said anode members extending in a direction parallel to the electron emitting surface of said cathode for a distance substantially equal to a multiple of a quarter wave length of the operating frequency of said device, and a radial transmission line connected to said anode structure, adjacent anode members being connected to opposite bounding surfaces only of said transmission line.

7. An electron discharge device comprising a cathode, an anode structure spaced from said cathode comprising a plurality of anode memn bers, each of said anode members extending in a direction perpendicular to the electron path between said cathode and said anode structure for a distance substantially equal to a multiple f a quarter wave length of the operating frequency of said device, a radial transmission line connected to said anode structure for coupling energy between said anode structure and said transmission line, adjacent anode members being connected to opposite bounding surfaces only of said transmission line, and means adjacent said anode structure for producing a magnetic field between said cathode and anode structure, and perpendicular to the direction of motion of electrons from said cathode to said anode structure.

8. An electron discharge device comprising a cathode, an anode structure spaced from said cathode, means for cooling said anode structure comprising coolant passages in said anode members, and a substantially parallel plane radial transmission line extending inwardly from said anode structure.

9. An electron discharge device comprising a cathode, an anode structure spaced from said cathode comprising a plurality of anode members, and a radial transmission line comprising a pair of substantially planar conductors extending outwardly from said anode structure for coupling energy between said anode structure and said transmission line, adjacent anode members being connected to opposite bounding surfaces only oi said transmission line.

10. An electron discharge device comprising a cathode, an anode structure spaced from-said cathode comprising a plurality of anode members, and a planar radial transmission line extending toward a center axis from said anode structure, adjacent anode members being connected to opposite bounding surfaces only of said transmission line.

li.. An electron discharge device comprising a cathode, an anode structure spaced from saidv cathode comprising a plurality of anode members, and a radial transmission line extending toward a center axis from said anode structure,

and connected to said anode members adjacentthe operating frequency of said device, means for cooling said anode structure comprising coolant passages in said anode members, and a radial transmission line extending inwardly from said anode structure, adjacent anode members being connected to opposite bounding surfaces only of said transmission line.

13. An electron discharge device comprising a cathode, an anode structure spaced from said cathode comprising a plurality of anode members, each of said anode members extending in a direction parallel to the electron emitting surface of said cathode for a distance substantially equal to a multi-ple of a quarter wave length of the operating frequency of said device, and a planar radial transmission line extending outwardly from said anode structure, adjacent anode members being connected to opposite bounding surf aces only of said transmission line.

14. An electron discharge device comprising a cathode, an anode structure spaced from said cathode comprising a plurality of anode members, each of said anode members extending in a direction perpendicular to the electron path between said cathode and said anode structure for a distance substantially equal to a multiple of a quarter wave length of the operating frequency of said device, and a planar radial transf mission line extending inwardly from said anode structure, adjacent anode members being con- 9 nected to opposite bounding surfaces only of said transmission line.

15. An electron discharge device comprising a cathode, an anode structure spaced from said cathode comprising a plurality of anode members, each of said anode members extending in a direction perpendicular to the electron path between said cathode and said anode structure for a distance substantially equal to a multiple of a quarter wave length of the operating frequency of said device, and a radial transmission line extending outwardly from said anode structure, and connected to said anode members adjacent the mid points thereof, adjacent anode 10 members being connected to opposite bounding surfaces only of said transmission line.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,414,085 Hartmann Jan. 14, 1947 2,444,419 Bondley July 6, 1948 2,446,825 Gurewitsch Aug, 10, 1948 2,446,826 McArthur Aug. l0, 1948 2,480,999 Brown et al Sept. 6, 1949 2,1925313 Okress Dec. 27, 1949 2,592,405 Brown Mar. 28, 1950 

